1. According to the basic halachah, one who searched for chametzand did not find any – his blessing is not considered in vain. This is because the blessing is recited about the mitzvah of searching itself [which the person fulfilled], and because the blessing also refers to the burning of the chametz which the person will fulfill in the morning. (Shulchan Aruch and Mishnah Berurah 432).
2. Nevertheless, there are those who have the custom of placing ten pieces of chametz [around the house] so that the person searching will find them. However, one must take the following precautions: (1) the pieces should be hard, such that they will not crumble [as an extra precaution, it is advisable to wrap them]; (2) they should be placed in locations that young children will not reach them; (3) the person who placed them should not forget where the pieces were placed, in case the person searching does not find all of them [for the same reason, it is advisable to write down the locations of all ten pieces] (ibid.).
